This invention relates to a process for recovering substantially pure 1,5- and/or 1,8-dinitroanthraquinone from dinitration mixtures.
It is known that the dinitration of anthraquinone produces mixtures consisting essentially of 1,5-, 1,8-, 1,6- and 1,7-dinitroanthraquinone. The separation of these mixtures has already been described in the literature, cf. DT-OS 2,143,253 (in oleum), Helv 14, 1404 (in monohydrate) and DT-OS 2,248,704 (in high-boiling organic solvents).
Unfortunately, these processes are unsatisfactory in terms of quality and/or yield, or on account of the large quantities of solvent required, or because production and separation have to be carried out in separate stages.
All these separation processes only yield a 1,5-dinitroanthraquinone which still contains at least 4.5 to 5 % by weight of 1,8-dinitroanthraquinone.
However, the presence of 1,8-dinitroanthraquinone in 1,5-dinitroanthraquinone in quantities as large as this is a troublesome factor in the production of products derived therefrom, for example the industrial-scale products 1,5-diaminoanthraquinone and 1-amino-5-benzoylamino-anthraquinone. Thus, all the 1,8-isomer remains in the 1,5-diaminoanthraquinone in the form of 1,8-diaminoanthraquinone after reduction. In the case of monobenzoylation, it remains in the 1-amino-5-benzoylamino anthraqinone in the form of 1-benzoylamino-8-aminoanthraquinone or 1,8-dibenzoylamino anthraquinone. So 1,8-substituted by products are extremely difficult and expensive to remove, in addition to which its removal involves heavy losses. If the 1,8-isomeric secondary products are not removed, their presence has an adverse effect in the production of dyes from 1-amino-5-benzoylamino anthraquinone by impairing the yields and/or colours and/or fastness. Accordingly, substantially complete removal of the 1,8-dinitroanthraquinone from 1,5-dinitroanthraquinone is of considerable commercial significance and is a problem to which, hitherto, there has been no economic solution.
Similarly, there has hitherto been no commercially and economically practicable process for the production of pure 1,8-dinitroanthraquinone. It is known that the commercially very important .alpha.,.alpha.-dinitration products of anthraquinone can be obtained in particularly high yields by nitration in concentrated nitric acid. Since the quantity of nitric acid required for this process is not appreciably higher than the quantity of sulphuric acid required for dinitration in H.sub.2 SO.sub.4, nitric acid is economically superior to dinitration in sulfuric acid. The much simpler regeneration of the solvent is another factor in favour of nitric acid. According to Moiseva (Org.Polyprod, i. Krasitel, Moscow 1969, No. 4, 70-79), it is possible by the nitric acid process to obtain a 1,5-dinitroanthraquinone in a yield of 30 % of the theoretical amount. However, it is not possible under the conditions quoted by Moiseva (98 % HNO.sub.3, 24 hours at 24.degree.-25.degree.C) to obtain pure 1,5-dinitroanthraquinone. Instead the products obtained still contain at least 5 % of 1,8-dinitroanthraquinone (cf. Example 18 below). Even under more stringent conditions (filtration under suction at elevated temperature, increasing the quantity of nitric acid used for washing), we were unable to obtain 1,5-dinitroanthraquinone with a purity of more than 95 % in a yield of more than 20 % of the theoretical amount. In addition, it is subsequently no longer possible to isolate pure 1,8-dinitroanthraquinone from the mother liquors, because they then contain too much 1,5-dinitroanthraquinone.
It has now been found that both pure 1,5-dinitroanthraquinone and also pure 1,8-dinitroanthraquinone can be isolated in good to very good yields from dinitration mixtures of anthraquinone by fractionation from nitric acid. In the context of the invention, dinitration mixtures are mixtures which consist essentially of 1,5- and 1,8-dinitroanthraquinone and which may additionally contain 1,6-, 1,7-, 2,6- and 2,7-dinitroanthraquinones or hydroxy dinitroanthraquinones and, to a small extent, other compounds which may even be free from nitro groups, such as anthraquinone. In general, the mixtures used as starting material will contain more than 50 % and preferably more than 60 % of 1,5- and 1,8-dinitroanthraquinone. The ratio of 1,5-dinitroanthraquinone to 1,8-dinitroanthraquinone can vary within wide limits and is by no means critical. In general, the mixtures used will have a ratio by weight of 1,5- to 1,8-dinitroanthraquinone of from 5 : 95 to 95 : 5. The proportion of ratio to one another of the aforementioned dinitroanthraquinones which may optionally be present in these dinitration mixtures consisting predominantly of 1,5- and 1,8 -dinitroanthraquinones is also not critical and can vary within wide limits.
The process according to the invention enables 1,5-and/or 1,8-dinitroanthraquinone to be obtained in pure form from dinitration mixtures of this kind, irrespective of how these dinitration mixtures have been obtained. For example, dinitration mixtures which have been obtained in known manner by the direct nitration of anthraquinone or 1-nitroanthraquinone, or mixtures of anthraquinone or 1-nitroanthraquinone can be used in the same way as, for example, dinitration mixtures which have been obtained by nitration of the secondary products accumulating during the purification of 1-nitroanthraquinone. It is also possible to use dinitration mixtures which have been obtained by mixing any products, solutions or suspensions of any origin which contain 1,5- and 1,8-dinitroanthraquinone. It is preferred to use dinitration mixtures of the kind obtained as reaction mixtures in the direct nitration of anthraquinone with concentrated nitric acid, optionally in the presence of strong acids, such as sulphuric acid or perfluoralkane sulphonic acids, such as perfluormethane or perfluorbutane sulphonic acid which may be used in a quantity of up to 20 % by weight, based on nitric acid. The reaction mixture thus obtained may be purified in accordance with the invention without any need for the reaction products to be further worked up, optionally after previous adjustment of the nitric acid concentration required for carrying out the process according to the invention, for example by distilling off concentrated nitric acid and/or by adding water or aqueous nitric acid.
In the process according to the invention, a crude 1,5-dinitroanthraquinone still containing about 5 to 30 %, preferably 8 to 15 %, of 1,8-dinitroanthraquinone is initially separated off and purified by treatment with highly concentrated nitric acid. Pure 1,8-dinitroanthraquinone is subsequently separated off from the mother liquors of the crude 1,5-dinitroanthraquinone. 1,5-Dinitroanthraquinone may be obtained in pure form independently form 1,8-dinitroanthraqinone. Thus, it is possible by the process according to the invention to prepare either only 1,5-dinitroanthraquinone without subsequently isolating the 1,8-dinitroanthraquinone, or to separate only 1,8-dinitroanthraquinone from dinitration mixtures without previously isolating the 1,5-dinitroanthraquinone. However, it is generally only advantageous to do this in cases where one of the two compounds to be separated is present in a large excess in a dinitration mixture of the kind in question. However, it is only possible to isolate pure 1,8-dinitroanthraquinone, without previously separating crude 1,5-dinitroanthraquinone, from mixtures of the kind which contain no more than 15% of 1,5-dinitroanthraquinone.
The invention provides a commercially advantageous method of obtaining 1,5- and 1,8-dinitroanthraquinone in yields and purities which, hitherto, it has not been possible to obtain in their isolation from nitric acid. In the case of 1,5-dinitroanthraquinone, the purity amounts to around .gtoreq.98 %.
The process according to the invention is carried out by adjusting in the dinitration mixture used a nitric acid concentration of from 91 to 96 %, preferably from 92.5 to 95.5 %, and a ratio by weight of nitric acid to solids of from 2.0 : 1 to 10 : 1, preferably from 2.5 : 1 to 10 : 1, at temperatures in the range of from 15.degree. to 50.degree.C, preferably from 20.degree. to 35.degree.C; separating off the insoluble crude 1,5-dinitroanthraquinone which still contains about 8 to 30 % of 1,8-dinitroanthraquinone, preferably after stirring for 1 to 15 hours; optionally washing it with 30 to 80 % by weight of 90 to 100 %, preferably 98 % nitric acid; subsequently treating the crude 1,5-dinitroanthraquinone with 90 to 100 %, preferably 98 to 100 % nitric acid in a ratio by weight of nitric acid to solids of from 0.5 to 3.5 : 1, preferably from 1 to 2 : 1; stirring the mixture for 1/2 to 40 hours at 0.degree.C to boiling temperature, more especially at 20.degree. to 70.degree.C; and separating off the insoluble pure 1,5-dinitroanthraquinone, optionally washing it with 95 to 100 %, preferably with 98 % nitric acid, followed by working up using methods known per se. In the context of the invention, the solids content is the total content of nitration products in the dinitration mixture used. This solids content is determined by methods known per se, generally by pouring part of the dinitration mixture into ice-water and then filtering the precipitate obtained under suction and washing it until neutral, followed by drying.
Pure 1,8-dinitroanthraquinone is separated off from the mother liquor of the crude 1,5-dinitroanthraquinone by adjusting a nitric acid concentration of from 88 to 94 % and a ratio of nitric acid to solids of from 3.0 : 1 to 12 : 1, preferably from 3.5 : 1 to 10 : 1, at temperatures in the range of from 20.degree. to 50.degree.C, and freed from the nitric acid adhering to it by methods known per se, the nitric acid concentration being adjusted in such a way that it is at least 1.5 % lower than in the preceding separation of 1,5-dinitroanthraquinone. Pure 1,8-dinitroanthraquinone obtained in this way only contains from 0.2 to 0.6 % of 1,5-dinitroanthraquinone. The yields of pure 1,5-dinitroanthraquinone amount to between 28 to 34%, and the yields of pure 1,8-dinitroanthraquinone to as much as 23 % of the stoichiometric yield.
In the separation of pure 1,5-dinitroanthraquinone, followed by the separation of 1,8-dinitroanthraquinone, it has proved to be advantageous either to separate the 1,5-dinitroanthraquinone at a nitric acid concentration of from 94 to 96 % and with a ratio by weight of nitric acid to solids of from 5.5 : 1 to 3.5 : 1 and, accordingly, to separate 1,8-dinitroanthraquinone at a nitric acid concentration of from 91 to 93 % and with a ratio by weight of nitric acid to solids of from 7 : 1 to 3.5 : 1, or alternatively to separate the 1,5-dinitroanthraquinone at a nitric acid concentraton of from 91 to 93 % and with a mixing ratio of nitric acid to solids of from 9.5 : 1 to 6.5 : 1 and, accordingly, to separate 1,8-dinitroanthraquinone at a nitric acid concenration of from 88 to 91 % and with a ratio by weight of nitric acid to solids of from 12 : 1 to 7 : 1. Accordingly, high acid concentrations correlate with high solids contents, whilst low acid concentrations correlate with low solids
In cases where nitration is carried out in nitric acid, the precipitation conditions for pure 1,8-dinitroanthraquinone can be adjusted, for example, by adding water or aqueous nitric acid, preferably with a concentration of greater than 65 %, or by distilling off nitric acid. For example, the nitration of anthraquinone with 5.5 to 12 parts by weight, preferably with 6 to 9 parts by weight, of 98 % nitric acid is best carried out by distilling off 15 to 35 % by weight and preferably 23 to 28 % by weight of 98 to 100 % nitric acid (based on the total weight of the mother liquor from the separation of the crude 1,5-dinitroanthraquinone) from the nitration mixture, preferably under reduced pressure at 50.degree. to 70.degree.C, followed by stirring after cooling, for example for 2 to 5 hours at 25.degree. to 30.degree.C. To establish the precipitation conditions by adding water, water is added at 20.degree. to 70.degree.C in a quantity of 20 to 27 ml per 100 g of anthraquinone used, or alternatively a nitric acid of corresponding water content is added. The addition is best accompanied by brief heating to 60.degree. to 75.degree.C until a clear solution is obtained, followed by stirring after cooling. quantity
By distilling off more nitric acid or by adding more water, optionally in the form of aqueous nitric acids, it is possible to obtain from the mother liquor of the pure 1,8-dinitroanthraquinone other defined fractions, for example a highly pure 1,5-and 1,8-dinitroanthraquinone mixture which contains less than 3 % of 1,6- and 1,7-dinitroanthraquinone. To this end, the mother liquor remaining after separation of the 1,8-dinitroanthraquinone may be concentrated by distilling off nitric acid to between 70 and 90 % and preferably to between 75 and 85 % of its original weight. Alternatively the mother liquor may be admixed with 4 to 6 ml of H.sub.2 O/100 g of filtrate or of an aqueous nitric acid of appropriate water content (where 1,8-dinitroanthraquinone has been obtained by distilling off nitric acid), or may be distilled to bewteen 70 and 80 %, preferably to 75 % of its original weight, or may be admixed with 5 to 7 ml of H.sub.2 O/100 g of filtrate (where 1,8-dinitroanthraquinone has been separated off by the addition of water). In this case, isolation is carried out at 20.degree. to 40.degree.C, preferably at room temperature, by stirring for between 1 and 24 hours, preferably for 2 to 3 hours, followed by washing with 65 to 90 %, preferably with 80 % nitric acid. Yields of from 14 to 17 % of the stoichiometric yield are obtained.
More than 90 % of the .alpha.,.alpha.-dinitroanthraquinones present in the original nitration mixture are thus obtained in 3 fractions. Residual 1,5- and 1,8-dinitroanthraquinones are present with almost all the 1,6- and 1,7-dinitroanthraquinone in the mother liquor of the 1,5-1,8-dinitroanthraquinone mixture. They can be separated off from the mother liquor with the 1,6- and 1,7-dinitroanthraquinone by continued distillation or by adding more water in such a way that almost all the 2,6- and 2,7-dinitroanthraquinones together with the hydroxy dinitroanthraquinones remain in solution in the filtrate.
To this end, the previously separated fractions, where they have been isolated by the partial distillation of nitric acid, are distilled to between 55 and 65 %, preferably to 60 %. Alternatively, where they have been isolated by the addition of water, 13 to 15 ml of water are added per 100 g of filtrate. The mixture is stirred for 1 to 3 hours on completion of distillation or after the water has been added and the precipitate is separated off at 20.degree. to 40.degree.C, preferably at 25.degree. to 30.degree.C. This gives a yield of 15 to 20 % of the theoretical of a mixture of which about 70 to 75 % consists of 1,6- and 1,7-dinitroanthraquinone (in substantially equal proportions) and which contains 18 to 25 % of 1,8-dinitroanthraquinone and 1 to 4 % of 1,5-dinitroanthraquinone. 2,6- and 2,7-dinitroanthraquinone and the hydroxy dinitroanthraquinones remain in the residual filtrates.
On completion of fractionation, it is thus possible to obtain in fractionated form from 90 to 95 % of the .alpha.,.alpha.- and .alpha.,.beta.-dinitroanthraquinones originally present in the reaction mixture.
Where the process according to the invention is used for the production of pure 1,5-dinitroanthraquinone, purification of the crude 1,5-dinitroanthraquinone yields an extract which contains almost exclusively 1,5- and predominantly 1,8-dinitroanthraquinone, and, optionally after the 1,8-dinitroanthraquinone has been separated off, a third fraction which also consists of 1,5- and, predominantly, 1,8-dinitroanthraquinone. These mixtures may be isolated as such and used for reactions. However, the extract and/or the third fraction may be introduced into the next dinitration batch of anthraquinone before or after the reaction without modifying the separation process according to the invention in any way. In this connection, the extract and/or third fraction can be isolated or subjected to intermediate drying, although this is not absolutely essential. In cases where both the extract and the third fraction are introduced in this way, the second dinitration results in almost complete separation of the .alpha.,.alpha.-dinitroanthraquinones into pure 1,5- and pure 1,8-dinitroanthraquinone, with the exception only of those fractions which are separated off with the 1,6- and 1,7-dinitroanthraquinone i.e. at most 10 to 15% of the .alpha.,.alpha.-dinitroanthraquinone present in the dinitration mixture. In this case, a mixture of 1,5- and 1,8-dinitroanthraquinone (known commercially by the name of Gloriamehl) is no longer obtained. In this way, it is possible to obtain up to 38 % of the stoichiometric yield of pure 1,5-dinitroanthraquinone and up to 32 % of pure 1,8-dinitroanthraquinone on a laboratory scale. On a commercial scale, it is possible to obtain yields of from 36 to 37 % of pure 1,5-dinitroanthraquinone and from 29 to 30 % of the stoichiometric yield of pure 1,8-dinitroanthraquinone.
Since, in this process, there is little or no increase in the total quantity of nitric acid used for dinitration of the anthraquinone, there is little or no increase in the consumption of nitric acid compared with separation into 1,5-dnitroanthraquinone containing 1,8-dinitroanthraquinone and pure 1,8-dinitroanthraquinone. This process can be carried out both during fractionation by removing the nitric acid by fractional distillation, and also by the fractional addition of water, optionally in the form of aqueous nitric acid.
It is clear that these processes (above all the last process, namely complete separation into 1,5- and 1,8-dinitroanthraquinone) can advantageously be carried out partly or completely continuously. In this case, the reaction and/or separation is carried out by a recycle process. Not only the extracts from the purificaton of 1,5-dinitroanthraquinone and/or the third fraction, but also the nitric acid distilled off during separation are returned to the reaction apparatus, optionally following partial or complete removal of the nitrous acid. The nitric acid used during nitration and any nitric acid lost during separation is replenished, for example by fresh nitric acid introduced during washing of the individual fractions or by fresh nitric acid introduced into the reaction. The water of reaction and the water additionally introduced during the washes or by the addition of water where separation is carried out by the fractional addition of water, remain in the sump of the 1,6- and 1,7-dinitroanthraquinone fraction or in the sump of the Gloriamehl fraction. The nitric acid in the sump can be recovered by distillation in the form of dilute nitric acid which can be used for washing. Alternatively it can be recovered by distillation using anhydrous H.sub.2 SO.sub.4 in the form of highly concentrated nitric acid which can be delivered to the reaction circuit.